Ultra wide band UWB communication systems refer to communication systems where the radio spectrum of the communication system is spread over a very wide frequency range compared to communication data speed. The technology is approaching commercial application, with various governments specifying permitted frequency ranges for the technology. The IEEE, specification body is in the process of establishing the standard IEEE 802.15.3. There are currently two proposals for the standard: one based on pulse radio technology and one based on OFDM (Orthogonal Frequency Division Method). The purpose of the UWB communication system standard is to increase the data throughput rate much higher than current wireless local area network (WLAN) data rates. The WLAN is standardized in the IEEE 802.11 and different versions of it.
Pulse radio ultra Wide Band (UWB) communications systems employ signals that are simply a very short pulse of RF frequency; a technology that has been explored since its origins in the 1960's.
Referring to FIG. 1A, there is shown a simplified sketch of a prior art transceiver. In the past, the classical transceiver contains a reference oscillator (synth) 34 which, as a rule, is stabilized with some reference crystal element 32 (Ref Osc). During reception, this frequency is subtracted from the received signal, and during transmission it is added to the data transferred (in up-down converter 20). Element 20 includes a channel filter which selects the operational RF channel. The RF signals pass through RF switch 15 to and from antenna 10. The RF switch 15 selects whether the transmission path or receiver path is connected to antenna 10. Band pass filter 12 filters out unwanted signals outside of the spectrum band of the system. The input and output signals are amplified by amplifiers 17 and 18.
Element 20 may include multiple down conversion, which is not shown in the figure in order to make figure simple. The filtered down converted RF signal is amplified with IF filters or baseband filters. The amplified signal is demodulated with module 35. Example 1A shows demodulation for an analog signal. The demodulation module 35 may include an analog-to-digital (AD) converter. Demodulation can be done also with digital signal processing (DSP). The information from demodulation circuitry is fed to baseband unit 50 that processes the detected information. In the case of digital data, the bits are converted to and from standard pulse levels and sent to or received from the relevant source or receiving units.
For UWB, the transmitter can be relatively simple compared with a narrow-band (NB) transmitter—the transmitter forms a pulse of a required shape and sends it to the antenna. FIG. 1B shows a pulse generator 42 connecting directly to RF switch 15. In case of reception, we amplify the signal in the same amplifier 17 as the narrow-band transceiver. The next module includes matched filter and correlator circuitry. The matched filter is optimally designed for the transmitted signal so that it optimizes the signal-to-noise ratio of the received signal. The correlator circuitry performs the detection of the received signal. The detected received signal is fed to baseband processor, denoted generally with numeral 50, which e.g. shows a received video signal to the display.
It is technically more difficult to detect a single pulse than a series of oscillations of the carrier frequency. Extensive work has been done in developing appropriate hardware, which is not a limit to the practical application of the invention described herein.
It is an advantageous feature of the invention that the UWB hardware is much simpler than NB transceivers and can be entirely assembled on a chip. An important advantage is that a UWB transmitter needs no analog part—a signal can be sent to the air right from the chip, and in case of reception this analog part is much simpler and can be realized within the frames of not only hybrid technologies but also base ones, i.e. CMOS and the like.
FIG. 2 illustrates graphs comparing the behavior of an UWB signal and a conventional narrow-band signal. On the upper left of the Figure, graph 220 shows a series of pulses, nominally one half cycle of an RF frequency, with a positive signal taken to represent a logic one and a negative signal representing a logic zero. On the lower left, a corresponding graph 210 shows a frequency shift as the distinguishing element, with a lower frequency compared with a nominal reference indicating a logic zero and a higher frequency indicating a logic one. A requirement for such a system is that the time duration of each bit is long enough that the receiver can reliably distinguish the logic states.
On the upper right, the frequency spectrum corresponding to the time signal is shown. Curve 225 shows a broad band covering the range from 3 GHz to 10 GHz (hence the name “ultra-wideband”). Typically, this very wide operational band is divided into smaller RF channels; having a channel bandwidth of around 528 MHz.
On the lower right, the time domain signal in graph 215 is confined within a relatively narrow band. In current communication systems: GSM bandwidth (BW) 273 kHz, IS-95 (=American CDMA) BW 1.25 MHz, WCDMA BW 3.84 MHz, WLAN 11 MHz. In the claims, the term “narrowband” will refer to a width of the communication system spectrum of the order of 10 MHz.
FIG. 3 shows a portion of the spectrum near the UWB band (3.1 GHz to 10.6 GHz). Bar 322 indicates the GPS band at 1.6 GHz, bar 324 indicates the PCS band at 1.9 GHz and bar 326 indicates the lower WLAN band (802.11b) at 2.4 GHz. There are several other systems working in the same 2.4 GHz band such as Bluetooth and cordless phones. Those skilled in the art will appreciate that harmonics of the foregoing bands will fall within the UWB range.
Further, the upper band for WLANs (band 802.11a) falls within the UWB range, denoted by bar 328. The frequency range is from 5.15 GHz up to 5.725 GHz.
Curve 310, representing UWB radiation, is shown as having a magnitude below the “Part 15 Limit”, referring to FCC regulation CFR-47 part 15. The UWB signal is required to be less than −41 dBm/MHz (a strength indicated by dotted line 330) in the specified signal range. There is not a formal requirement of signal strength below 3.1 GHz, but workers in the field assume that a limit of −61 dBm/MH is appropriate, in view of the sensitivity of GPS receivers to interference.
In the commercial marketplace, UWB applications include:
High Speed (20+ Mb/s) LAN/WANs
Altimeter/Obstacle Avoidance Radars (commercial aviation)
Collision Avoidance Sensors
Tags (Intelligent Transportation Systems, Electronic Signs, Smart Appliances)
Intrusion Detection Radars
Precision Geolocation Systems
Industrial RF Monitoring Systems
The second alternative UWB standard proposal is based on OFDM, which is shown in the FIG. 9. The UWB proposal based on OFDM has been proposed by the multiband OFDM consortium (http://www.multibandofdm.org/). The OFDM technology is well established, having been invented more than 40 years ago. OFDM has been adopted by several standards: Asymmetric Digital Subscriber Line (ADSL) services, VDSL, Digital Audio Broadcast (DAB), Digital Terrestrial Television Broadcast: DVB in Europe and ISDB in Japan. The WLAN standards IEEE 802.11a/g, 802.16a are based on OFDM.
Because OFDM is suitable for high data-rate systems, it is also currently being considered for the following standards: Fourth generation (4G) wireless services and IEEE 802.11n and IEEE 802.20.
The OFDM is a sub carrier modulation in which the original data has been divided into several smaller data streams. In the proposed UWB specification the 528 MHz radio channel is divided to 128 sub-carriers.
The same radiation power specifications apply to both UWB standard proposals.
Since frequency approval for UWB operation has yet to be acted upon by the Federal Communications Commission (FCC), there are currently no “approved” applications within the United States.